1. Field of the Invention
The present invention relates to an active-matrix type liquid crystal display device having a switching element for each pixel, and more particularly to a dot-inversion type liquid crystal display device which supplies voltages of different levels to the two switching elements corresponding to adjacent pixels.
2. Discussion of the Background
Thin Film Transistor (TFT) type liquid crystal display devices comprise a switching element and a pixel electrode (display electrode) for each of their pixels. Such devices are constituted in order that a transmittance of a liquid crystal layer changes depending on a voltage applied to the pixel electrode. One end of the switching element is supplied with a voltage in accordance with pixel data, and a voltage of the pixel electrode is controlled in accordance with the voltage applied to the switching element.
Unchanged application of a voltage in the same direction to the liquid crystal layer gives rise to fixing of an arrangement of the liquid crystal, resulting in a slow motion of the liquid crystal and blackish displaying. Therefore, in order to cope with such problem, a liquid crystal display device adopting an inversion driving type, which allows the voltage applied to the liquid crystal layer to make an inversion in one frame unit (one screen), in one horizontal line unit or in one pixel unit, has been proposed. As shown in FIG. 1 and described below, a positive side analog voltage is applied to a first pixel of the liquid crystal layer and a negative side analog voltage is applied to an adjacent pixel. Because separate voltages are generated, the associated circuit may introduce time delays between these signals. Also such a circuit may process pixel data having a large number of bits. Thus the circuit may have a large power consumption for processing such data.
For portable equipment driven with a battery, such as notebook type computers and electrical pocketbooks, lengths of driving time of the battery are essential factors which determine the added values of products, and products with a battery having a short life because of a large power consumption have a low commercial value, resulting in a lack of the competitive power in many cases.